Present systems that measure the condition of a medium, such as water, oil, gas, air, etc., rely upon detection devices, such as flow meters, leak detectors, pressure sensors, etc., that are attached to the outside of the infrastructure carrying the medium so that data collected by the sensors may be transmitted to a separate communication device, such as an antenna that transmits the data through a different medium, such as open space, some short range to another devices, that passes the data along to some central monitoring system.
For example, water leak detection units for detecting leaks in municipal and residential water pipes typically rely upon some type of sensor, such as accelerometer or microphone, which is attached to the pipe and listens to vibrations within the pipe. The leak detector may then be attached to an endpoint device, such as in a metal or plastic pit installed in the ground, which is then connected to an antenna that transmits data from the sensor to a central system, probably through one or more intermediary devices. Such detectors may be relatively inexpensive fixed systems, in exchange for poorer performance and a short transmission range, or very expensive transient systems, in exchange for moderately better performance, but which still tend to have a short transmission range.
Some of the issues associated with such systems include: (1) low received sensitivity due to transverse measurements; (2) strong pipe effects due to the sensor measuring the convolution of the pipe's self-resonance along with the vibrations in the water; and (3) a poor environment for a fix wireless communications network. With regard to this later issue, consider that the typical leak detector and endpoint devices are installed in a pit, generally submerged by water, surrounded by reinforced concrete, and covered with a metal plate for a lid on the pit. Radio frequency (RF) propagation to a central system or intermediary device in such an environment is very difficult. At 915 MHz, even a plastic lid can result in 6 dB of loss, with a solid metal lid resulting in as much as 25 dB of loss. Transmission can be improved, marginally, by placing an antenna outside of the pit and above the lid, but doing so requires a custom cable for transmission of the RF signals from the endpoint to the antenna, and placing the antenna above ground leaves the antenna susceptible to environmental damage and conditions, vandalism, theft, etc. Leak detectors in such environments are also generally separated from other types of detectors, such as a flow meter or pressure sensor.
While a water supply system is described above, sewage, oil and gas transmission lines, industrial applications, and many other types of similar systems experience similar shortcomings to those described herein.